The Evolved Packet System (EPS) of the 3rd Generation Partnership Project (3GPP) is composed of an Evolved Universal Terrestrial Radio Access Network (E-UTRAN), a Mobility Management Entity (MME), a Serving Gateway (S-GW), a Packet Data Network Gateway (P-GW, PDN GW), a Home Subscriber Server (HSS), a 3GPP Authentication Authorization Account (AAA) server, a Policy and Charging Rules Function (PCRF) entity and other support nodes.
FIG. 1 is a structural diagram of the existing EPS system in the related art. As shown in FIG. 1, in this structural diagram, the MME is responsible for the related work at the control plane, such as mobility management, processing of non-access stratum signaling and management of user mobile management context. The S-GW, which is an access gateway device connected to the E-UTRAN, is used to forward data between the E-UTRAN and the P-GW and is responsible for caching paging waiting data. The P-GW, which is a border gateway between the EPS and a Packet Data Network (PDN), is responsible for functions, such as access of the PDN and forwarding of data between the EPS and the PDN.
The EPS supports the interworking with the non-3GPP network, i.e., it implements the interworking with the non-3GPP network through S2a/b/c interfaces. The non-3GPP network includes the trusted non-3GPP network and untrusted non-3GPP network. The Internet Protocol (IP) access of the trusted non-3GPP network can be directly connected to the P-GW through an S2a interface; the IP access of the untrusted non-3GPP network is required to be connected to the P-GW through an Evolved Packet Data Gateway (ePDG), which is connected to the P-GW through an S2b interface.
If the EPS system supports Policy and Charging Control (PCC), then the PCRF makes policy and charging rules. The PCRF is connected to an IP service network of an operator through a receiving interface Rx, and obtains service information. In addition, the PCRF, connected to a gateway device in the network through Gx/Gxa/Gxc interfaces, is responsible for initiating the establishment of an IP bearer, ensuring the Quality of Service (QoS) of service data, and performing charging control. The Policy and Charging Execution Function (PCEF) is situated in the P-GW, and the PCRF exchanges information with the P-GW through a Gx interface. When an interface between the P-GW and the S-GW is based on Proxy Mobile IP (PMIP), Bearer Binding and Event Report Function (BBERF) exists in the S-GW, and the S-GW exchanges information with the PCRF through a Gxc interface. Upon access through the trusted non-3GPP network, the BBERF also resides in a trusted non-3GPP access gateway, the access gateway of the trusted non-3GPP network exchanges information with the PCRF through a Gxa interface. When a User Equipment (UE) is roaming, an interface between a home PCRF and a visited PCRF is an S9 interface, while an Application Function (AF) providing services for the UE is situated in a service network and sends service information used for generating the PCC policy to the PCRF via an Rx interface.
In the existing technology, a protocol used in a PCC architecture is a Diameter application protocol developed based on the Diameter Base Protocol, such as an application protocol applied to a Gx interface, an application protocol applied to an Rx interface, an application protocol applied to a Gxx interface (including Gxa and Gxc interfaces) and an application protocol applied to a roaming interface S9. Messages, commands and Attribute Value Pairs (AVP) used for the PCC are defined in these application protocols. Diameter sessions established using these protocols may be called as Gx session, Gxx session, Rx session and S9 session, respectively. Various function entities of the PCC perform, through these sessions, policy and charging control on a PDN connection established for the UE to access to the network. Generally, one IP connection from the UE to the PDN network is called as one IP Connectivity Access Network (IP-CAN) session. One important operation executed by the PCRF is to link the Gx session, gateway control session (Gxx session) and S9 session performing policy control on the same IP-CAN session to each other. The linking operation is performed during establishment and modification of the IP-CAN session. The above Diameter sessions are called herein as policy and charging control session.
FIG. 2 is a flow chart of an initial attachment process in which a UE accesses to the EPS via the E-UTRAN and establishes a PDN connection (i.e., IP-CAN session). The PMIPv6 protocol is used between an S-GW and a P-GW. The process shown in FIG. 2 mainly comprises the following steps.
Step S201, the UE sends an attachment request message to an eNodeB (envolved NodeB, eNB for short) to request access to to the EPS.
Step S202, the eNodeB sends the attachment request message to an MME.
Step S203, a network authenticates the UE and starts Non-Access Stratum (NAS) security encryption protection.
Step S204, the MME interacts with a HSS after the authentication of the UE is passed, and performs a location update process.
Step S205, the MME selects the P-GW for the UE based on a default Access Point Name (APN) subscribed by a user, selects an S-GW, and sends an establishment default bearer request message to the selected S-GW; “APN” is used to denote the “default APN” hereinafter in the case of no ambiguity.
Step S206, a BBERF located in the S-GW sends a gateway control session establishment indication message containing a user identifier NAI (Network Access Identifier), a PDN identifier APN and a bearer attribute of the current access network to a PCRF; the gateway control session (Gxx session) that this message requests to establish is denoted as Gxx session1.
The bearer attribute of the access network includes IP-CAN type and BBERF address; in addition, the bearer attribute of the access network may further include Radio Access Technology (RAT) type.
Step S207, the PCRF obtains subscription information of the user based on the user identifier NM and the PDN identifier APN so as to make policies based on the subscription information of the user, the network policies, and the bearer attribute (including IP-CAN type, or IP-CAN type and RAT type) of the current access network. At this point, the policies made by the PCRF are the default policies for the user to access to this APN, including PCC rules, QoS rules and an event trigger.
The PCRF returns a gateway control session establishment acknowledgement message to the BBERF, and sends the made QoS rules and the event trigger to the BBERF; and the BBERF installs and performs the QoS rules and the event trigger.
Step S208, the S-GW sends a proxy binding update message containing the user identifier NM, the PDN identifier APN and the bearer attribute (including IP-CAN type, or IP-CAN type and RAT type) of the access network to the P-GW selected by the MME in step S205.
Step S209, the P-GW allocates an IP address, which is denoted as IP Address1, to a PDN connection that is requested to be established by the UE for access.
The PCEF located in the P-GW sends an IP-CAN session establishment indication message containing the user identifier NAI, PDN identifier APN, IP Address1, and bearer attribute (including IP-CAN type, or IP-CAN type and RAT type) of the access network to the PCRF; the bearer attribute of the access network in this message is obtained in step S208; the Gx session that this message request to establish is denoted as Gx session1.
Step S210, the PCRF links Gxx session1 to Gx session1 based on the NAI and APN, i.e., Gxx session1 and Gx session1 are used for performing policy and charging control on the PDN connection (i.e., IP-CAN session) which is requested to be established by the UE.
Step S211, the PCRF returns an IP-CAN session establishment acknowledgement message to the PCEF, and sends the PCC rules and the event trigger made in step S207 to the PCEF; the PCEF installs and performs the PCC rules and the event trigger.
The PCRF might modify the PCC rules and QoS rules based on the bearer attribute of the access network reported in step S209, and at this point, the PCRF will send the modified PCC rules and QoS rules to the PCEF and BBERF respectively for updating.
Step S212, the P-GW returns a proxy binding acknowledgement message containing IP Address1 to the S-GW.
Step S213, the S-GW returns an establishment default bearer reply message containing IF Address1 to the MME.
Step S214, the MME returns an attachment acceptance message containing IP Address1 to the eNodeB.
Step S215, the eNodeB returns the attachment acceptance message containing IP Address1 to the UE.
Step S216, the UE sends an attachment completion message to the eNodeB.
Step S217, the eNodeB sends the attachment completion message to the MME.
Step S218, the MME and the S-GW perform an interaction process of updating the bearer.
Step S219, the MME knows that the UE can access through the non-3GPP system based on the subscription information of the user, and thus sends the address of the P-GW selected when the UE establishes the PDN connection (i.e., IP-CAN session) to the HSS, which stores the address of the P-GW and then returns a reply message.
The UE establishes the PDN connection (i.e., IP-CAN session) to the default APN through the process shown in FIG. 2; afterwards, the UE can access dedicated services through this connection. The PCRF will make the PCC rules and QoS rules based on information, such as service features, the subscription information of the user, the network policies and the bearer attribute of the access network. Since the linking is performed in step S210, the PCRF can send the PCC rules to the PCEF via Gx session1 and sends the QoS rules to the BBERF via Gxx session1. When the BBERF requests new QoS rules or modifies the QoS rules via Gxx session1, the PCRF will also make the corresponding PCC rules or modify the corresponding PCC rules, and send the corresponding PCC rules to the PCEF via Gx session1; or vice versa.
When handover across systems or handover across S-GWs (i.e., BBERF reselection) occurs in the UE, the PCRF is required to perform a new linking operation.
FIG. 3 is a flow chart of handover from the E-UTRAN to the trusted non-3GPP access system after a UE accesses to the EPS using the process shown in FIG. 2. In the case of the non-3GPP access, the PMIPv6 protocol is used between a trusted non-3GPP access gateway and a P-GW. The process shown in FIG. 3 mainly comprises the following steps.
Step S301, the UE establishes a PDN connection (i.e., IP-CAN session) through the 3GPP access, and there is a PMIPv6 tunnel between the S-GW and the P-GW.
Step S302, the UE finds the trusted non-3GPP access system and decides handover of the current session from the 3GPP access system to the trusted non-3GPP access system.
Step S303, the UE, trusted non-3GPP access gateway and HSS/AAA perform an Extensible Authentication Protocol (EAP) authentication process, in which the HSS/AAA returns the address of the P-GW selected by the UE during the 3GPP access to the trusted non-3GPP access gateway.
Step S304, a layer 3 attachment process specific to the non-3GPP access is triggered upon success of the authentication; in this process, the UE indicates the network that the UE has IP address keeping capability.
Step S305, a BBERF located in the trusted non-3GPP access gateway sends a gateway control session establishment indication message containing a user identifier NM, PDN identifier APN and bearer attribute (including new IP-CAN type, or new IP-CAN type and new RAT type) of the current access network to a PCRF; the gateway control session (Gxx session) that this message requests to establish is denoted as Gxx session2.
Step S306, the PCRF links Gxx session2 to Gx session1 established in the process shown in FIG. 2 based on the NAI and APN.
Step S307, the PCRF makes QoS rules and an event trigger, including the dedicated policy made by the PCRF for the UE when the UE accesses the dedicated service through 3GPP access, for the UE to access through the 3GPP system based on subscription information of a user, network policies, and the bearer attribute of the current access network.
The PCRF sends the above QoS rules and event trigger to the BBERF through a gateway control session establishment acknowledgement message; the BBERF installs and performs the QoS rules and the event trigger; the trusted non-3GPP access gateway performs the specific non-3GPP access process for resource reservation.
Step S308, the trusted non-3GPP access gateway sends a proxy binding update message containing the user identifier NAI, the PDN identifier APN and the bearer attribute (including IP-CAN type, or IP-CAN type and RAT type) of the current access network to the corresponding P-GW based on the address of the P-GW obtained in step S303.
Step S309, the P-GW allocates an IP address (i.e., IP Address1) used when the UE accesses to the network via the 3GPP system to the UE based on the NAT and APN so as to keep the IP address unchanged and further ensure the service continuity.
The PCEF located in the P-GW sends an IP-CAN session modification indication message containing a new bearer attribute of the access network obtained in step S308 to the PCRF; modified by this message is Gx session1 established in the process shown in FIG. 2.
Step S310, the PCRF determines that handover (i.e., handover from the 3GPP to the non-3GPP) occurs in the tunnel of the PDN connection (i.e., IP-CAN session) established by the UE, and therefore, the PCRF modifies the PCC rules for the reestablished PDN connection (i.e., IP-CAN session) based on the new bearer attribute of the access network, and returns the modified PCC rules to the PCEF through an IP-CAN session modification acknowledgement message for updating.
Step S311, the P-GW returns a proxy binding acknowledgement message containing IP Address1 to the trusted non-3GPP access gateway.
Step S312, the trusted non-3GPP access gateway returns a layer 3 attachment completion message containing IP Address1 to the UE.
Step S313, the UE performs the handover of the PDN connection from the 3GPP access to the trusted non-3GPP access, and there is a PMIPv6 tunnel (this PMIPv6 tunnel is established in steps S308 and S311) between the trusted non-3GPP access gateway and the P-GW; all the services accessed by the UE through the 3GPP access can be continued to be accessed.
It can be seen from the process shown in FIG. 3 that the PCRF links the new Gxx session to one established PDN connection (IP-CAN session) based on the NM and APN, and the PCRF can further update the policies made by the PCRF when the UE access through the 3GPP system based on the new bearer attribute of the access network to send to the new BBERF through the new gateway control session (Gxx session), thereby ensuring that the non-3GPP access system has performed resource reservation for services that are previously accessed by the UE before the handover occurs in the PMIPv6 tunnel (i.e., before step S308), and thus the handover speed is accelerated, and the user experience is improved.
However, not all UEs can perform the handover process (i.e., keep the IP address unchanged). When the network is not sure whether the UE has the network mobility capability (i.e., the IP address keeping capability), the P-GW decides whether to allocate a new IP address (i.e., establish a new PDN connection) to the UE or keep the IP address unchanged (i.e., handover of the established PDN). However, the P-GW makes this decision after receiving the proxy binding update message sent by the trusted non-3GPP access gateway. At this point, the PCRF has made a decision of linking the new gateway control session (Gxx session) to the existing PDN connection (i.e., the PCRF has made the decision of handover). If at this point the P-GW decides to establish a new PDN connection without handover, then the inconsistency of the policy sent by the PCRF with the decision of the p-GW will be certainly resulted in, causing occurrence of errors. A method for solving this problem in the existing technoly will be described below.
(1) When the access gateway is unable to determine whether the UE has the network mobility capability, a gateway control session establishment indication message containing a deferred linking indication is sent to the PCRF by the BBERF located in the access gateway. The PCRF does not immediately link the established gateway control session (Gxx session) (i.e., Gxx session2 in FIG. 2) to the existing PDN connection (IP-CAN session) after receiving the deferred linking indication.
(2) If the P-GW decides to perform handover, the PCEF located in the P-GW sends an IP-CAN session modification indication message to the PCRF to modify the established Gx session (i.e., Gx session1 in FIG. 3), and, at this point, links the newly established gateway control session (Gxx session) (i.e., Gxx session2) to the established PDN connection (IP-CAN session) (i.e., links Gxx session2 to Gx session1).
(3) If the P-GW decides to establish newly one PDN connection (IP-CAN session) instead of performing the handover, then the P-GW allocates a new IP address (which is denoted as IP Address2) to the UE. The PCEF located in the P-GW sends an IP-CAN session establishment indication message containing the user identifier NAI, the PDN identifier APN and IP Address2 to the PCRF to request to establish a new Gx session (which is denoted as Gx session2). At this point, the PCRF decides to link the newly established gateway control session (Gxx session) to the newly established Gx session (i.e., links Gxx session2 to Gx session2). In this case, the dedicated services that are previously accessed by the UE through the 3GPP access will be interrupted, thus the UE is required to reinitiate a service request, and the PCRF remakes the policies for the UE.
The above way of not immediately linking the established gateway control session to the existing PDN connection is called as deferred linking.
Only a method for implementing session deferred linking of policy and charging control in a non-roaming scenario is discussed in the existing technology. A roaming scenario has not yet involved in the existing technology.
There are two roaming architectures for the EPS, the first one is home routed, and the second one is local breakout. FIG. 4 is a roaming structure diagram of the EPS for home routed in the existing technology. As shown in FIG. 4, a P-GW is in a home network, and IP services are provided by a home network operator (i.e., an AF is in the home network). FIG. 5 is a roaming structure diagram of the EPS for local breakout in the existing technology. As shown in FIG. 5, a P-GW is in a visited network, and IP services can be provided by a home network operator (i.e., an AF is in a home network) or a visited network operator (i.e., an AF is in the visited network). For different roaming scenarios, processes of the PCC are different, and functions performed by PCC network elements are also different.
At present, in a scheme for implementing an S9 roaming interface, a Visited PCRF (vPCRF for short) terminates Gx sessions and gateway control sessions (Gxx sessions) of all IP-CAN sessions established by the UE existing in the visited network, i.e., establishes one S9 session between the vPCRF and a Home PCRF (hPCRF) instead of sending the gateway control sessions (Gxx sessions) and Gx sessions to the hPCRF, and transmits information on the Gx sessions and Gxx sessions of all the IP-CAN sessions using this S9 session. However, the vPCFF does not terminate the Rx sessions of all the IP-CAN sessions in the visited network, and only forwards messages of the Rx sessions to the home PCRF, and uses the vPCRF as one proxy. A plurality of subsessions (which is called as S9 Subsession) might exist in one S9 session, each subsession being used for transmitting information on the Gx session and gateway control session (Gxx session) of one IP-CAN session.
In summary, due to the complexity of the roaming scenarios of the EPS and the complexity of deferred linking of the policy and charging control session itself in the roaming scenario, there are difficulties in the method for implementing the deferred linking of the policy and charging control session and the policy and charging control thereon, and there has not a corresponding solution yet in the existing technology.